Conventional propulsion units for marine vessels include, inboard drives, outboard drives, and sternboard drives. Sternboard drives (often referred to as a “sterndrive”) are popular in recreational marine vessels. With a sterndrive vessel, an internal combustion or diesel engine resides inside the hull of the vessel and the drive is mounted to the transom of the vessel. However, conventional existing drives have many disadvantages. For example, a drive shaft must connect the internal combustion engine with the drive and penetrate the transom to transmit power to the sternboard drive. This requires a sizable hole through the transom or hull that weakens the transom and provides a potential leak path. Furthermore, the engine, which must be mounted adjacent to the transom, takes up a large amount of space in the hull that could be used for other purposes such as for passengers or storage. The engine also adds a significant amount of weight in the rear of the vessel that requires ballast elsewhere in the vessel for balancing, handling and operational stability of the vessel. Combustion engines also require frequent maintenance to keep them operating properly, and they produce harmful emissions, excessive noise, and undesirable fumes and odors.
The present invention pertains to a propulsion drive mounted to the transom of a marine vessel whereby the means of propulsion is an electric motor that forms a part of the drive. This invention is an improvement to an existing sternboard drive, which is typically driven by a shaft that penetrates the transom and is powered by an internal combustion or diesel engine located inside the vessel.
Electric outboard motors have been available for many years. An electric outboard motor is a one-piece unit that is removable and can be attached to a transom usually by a clamping system. An electric outboard can be steered by hand or through a steering mechanism. One example is an electric outboard drive discussed in U.S. Pat. No. 8,529,305 to Lin. This invention describes an electric outboard drive adapted to be mounted on a transom of a boat through a mounting bracket and includes a driving device and a propelling device. In contrast, the present invention teaches a watertight, transom mounted, permanent electric marine sterndrive propulsion drive unit mounted to an external surface of the transom of a marine vessel comprising an integrated electric motor.
In a more recent attempt at incorporating an electric motor, U.S. Pat. No. 8,333,626 to Daikoku teaches the use of a hybrid outboard motor that includes an internal combustion engine and an electric motor wherein the power plant is encased in a watertight box or casing that is attached to the external surface of the transom. While Daikoku incorporates an electric motor, he incorporates the electric motor with a conventional internal combustion engine that resides within the hull of the vessel.
While others have developed electric recreational boats with sterndrive units, they place the electric motor inside the hull of the vessel much like the placement of an internal combustion engine.
All of the above conventional arrangements suffer from one or more of the same drawbacks. In contrast, the present invention solves the above deficiencies by integrating an electric motor on the outside of the hull as a one-piece unit. In placing the electric motor outside of the hull, the present invention does not require the placement of a driveshaft through the hull, nor does it require placement of an internal combustion engine, or electric motors, within the hull. Without an internal combustion engine adjacent to the transom, there is no need to provide offsetting ballast to compensate for the weight of an internally positioned engine. While the sterndrive of the present invention adds the weight of a sterndrive-mounted electric motor, the battery packs can be positioned within the hull to offset the weight and maximize performance and stability of the vessel.